There are several reasons why horses can be underweight. If your horse is underweight make sure it has been de-wormed and had its teeth checked by a veterinarian or equine dentist before simply adding more feed to its diet.
Food alone may not be the whole of the problem if you’re having difficulties putting weight on your horse. Bad teeth can make it painful for the horse to chew, cause the horse to swallow poorly masticated food, or make it chew very slowly. Internal parasites may also be stealing nutrition from your horse as well as damaging internal organs.
Be sure that other horses aren’t preventing your horse from getting to the food, and that external pests like biting insects aren’t causing it to burn off energy trying to get relief. Once you’ve eliminated all the external reasons why your horse is underweight, look at the food you are giving it.
Best Feed for Underweight Horses
The best feed for an underweight horse is good quality hay or pasture grass. Give them free choice hay unless there is some medical reason (such as diabetes or Cushing’s Disease) not to. Introduce horses to lush grass gradually to decrease the possibility of founder or colic. Most horses do very well on grass or hay alone. More hay in its feeder or longer grazing time may be all it takes to see weight gain.
Grass hay and pasture grasses are often sufficient for weight gain but alfalfa and other legume hays help boost the richness of hay and pasture. Go slowly when introducing any new feed to your horse even if it is "only hay."
Extra Feeds For Skinny Horses
Beet pulp is often fed as a supplement because it is high in fiber, which the horse can turn into energy and body fat. Some people prefer to give their horses pelleted feed because they feel this is more easily digestible. Older horses might be able to digest "cooked" grains easier than regular grains, so a specially prepared senior feed might be helpful. For horses with bad teeth, smaller pellets or grains are easier to chew than larger pellets or cubes. Rice bran and flax are also popular additions to the diets of underweight horses. Contrary to popular belief, flax seed is not harmful. The amount of toxin is so minute it has no effect. Flax is best fed ground. Grind it within a short time of feeding so the natural oils in the seed don’t spoil.
Oils such as bran, rice, corn, flax, and other grain oils are often used to boost the energy and calories of a horse’s feed. Some people feel they also help keep the horse’s skin healthy and coat shining. Go carefully when adding these oils to your horse’s diet, as like any other "high octane" fuels they could give problems if fed in large amounts or too quickly. Too much oil in the diet can also cause diarrhea.
Whenever you are changing the number of concentrates, do it gradually to decrease the possibility of problems like founder or colic. Whatever combination you feed, 60 percent of a horse’s diet should be roughage in some form. If a change in your feeding program does not produce some small gain in weight or energy within about 10 days, consult your veterinarian. There could be an underlying problem like ulcers or other digestive diseases that is causing weight loss.